Tiletamine/zolazepam for anaesthetic induction in colic horses. A retrospective evaluation

Scopo del lavoro Tiletamine/zolazepam (TZ) combination is widely used as an induction agent in horses undergoing elective surgeries (1), but it has never been described in colic horses. The aim of this study was to retrospectively evaluate the effects of TZ for anaesthesia induction in horses undergoing surgery for colic syndrome and to compare them with the most used ketamine and benzodiazepine (KB) combination. Materiali e metodi The anaesthesia records of horses referred for surgical colic syndrome between 2021 and 2024 were reviewed. Only the complete records of adult horses without co-existing diseases requiring surgical intervention were considered. The following data were evaluated: signalment, American society of anaesthesiology (ASA) physical status, premed- ication protocol, length and quality of induction (scale 0 to 3), anaesthesia duration, length and quality of recovery (scale 1 to 5), incidence of complications, inotrope and/or vasopressor administration. The average intraoperative heart rate (HR), mean arterial pressure (MAP) and fraction of expired isoflurane (FEIso%) were calculated. Horses were divided into two groups according to the induction protocol: KB group (ketamine 2.5 mg/kg plus diazepam / midazolam 0.05 mg/kg) and TZ (tiletamine-zolazepam 1 mg/kg). Data were assessed for normal distribution (Shapiro Wilk test). A Student’s T-test or a Wilcoxon test was used for comparison between the groups. Categorical data were compared using a Fisher’s exact test. Normally distributed data are presented as mean ± standard deviation (SD); non-normally distributed data are presented as median and range. A p value <0.05 was considered statistically significant. Risultati One hundred and two anaesthetic records were collected, of which only 35 met the inclusion criteria. Seventeen horses were included in the KB group (10 female, 4 male and 3 geldings) with a mean age of 15 ± 8 years, a mean weight of 471 ± 55 kg and a median ASA status of 3 (2-5). Eighteen horses were included in the TZ group (7 female, 7 male and 4 geldings) with a mean age of 14 ± 6 years, a mean weight of 538 ± 75 kg and a median ASA status of 3 (2-4). The mean weight of the TZ group was significantly higher than that of the KB group (p= 0.005). The mean anaesthesia was 159 ± 43 minutes in the KB group and 183 ± 49 minutes in the TZ group and the difference was not statistically significant. All horses were premedicated intravenously with romifidine and butorphanol. Partial intravenous anaesthesia con- sisting in isoflurane and romifidine infusion was used for maintenance, and romifidine was also administered at the recovery. The median induction time and induction score did not differ significantly between the two groups. Induction was achieved in 65 (30-120) seconds in the KB group and in 70 (40-200) seconds in the TZ group. The median induction score was 3 (0-3) in both groups. The induction was obtained with the aid of a gate in all the horses except in one in the KB group, where it was manually assisted. The median recovery time and recovery score did not differ significantly between the two groups. Median recovery time was 60 (25-540) minutes and 85 (50-100) minutes for the KB and TZ groups respectively. The median recovery score was 2 (1-4) in the KB group and 2 (1-3) in the TZ group. Assisted re- covery with ropes was required in 1/7 and 4/18 horse in the KB and TZ group respectively. Intraoperatively, the mean FEIso% was 1.2 ± 0.1% in both groups; the median HR was 38 (30-81) beats/min in the KB group and 39 (33-82) 169 31° CONGRESSO INTERNAZIONALE 22/23-24 GENNAIO 2026 - FIRENZE beats/min in the TZ group. The mean MAP was 79 ± 11 mmHg in the KB group and 83 ± 11 mmHg in the TZ group. Dobutamine was administered intraoperatively in 16/17 KB horses [median dose 1 (0-6) mcg/kg/min] and in 17/18 TZ horses [median dose 0.5 (0-1.6) mcg/kg/min]. Norepinephrine was administered in 2 horses of each group and ephedrine in 4/17 and in 1/18 horses in KB and TZ group respectively. Hypotension (KB n=14; TZ n=11), hypercapnia (KB n=6; TZ n=7) and hypoxia (KB n=5; TZ n=3) were observed in both groups but their incidence was not signifi- cantly associated with the induction protocol. One horse in the KB group died at the recovery from cardiac arrest. Conclusioni The results of this study demonstrate that TZ used for anaesthesia induction in colic horses provides induction, main- tenance and recovery conditions comparable to the most used ketamine and benzodiazepine combination as previously described in horses undergoing elective surgeries (2). It is worth noting, that the quality of recovery in these colic horses was worse than that described in non-colic horses receiving a similar anaesthetic protocol (2). However, many horses in both groups, developed hypotension, hypercapnia or hypoxia which are common in colic due to the poor pre-existing clinical conditions, and they can be potentially detrimental on the recovery quality (3). Bibliografia 1. Hubbell et al (2025) A review of equine anesthetic induction: Are all equine anesthetic inductions «crash» inductions? J Equine Vet Sci 139:105130. 2. Lambertini et al (2024) Comparison of Ketamine/Diazepam and Tiletamine/Zolazepam Combinations for Anaesthesia Induction in Horses Undergoing Partial Intravenous Anaesthesia (PIVA): A Retrospective Clinical Study. Vet Sci 11:612. 3. Gozalo-Marcilla et al (2021) Recovery after General Anaesthesia in Adult Horses: A Structured Summary of the Literature. Animals; 11:1777.